1. Field of the Invention
This invention relates to an epoxy resin curing agent, an epoxy resin composition containing the curing agent, and a cured product of the epoxy resin composition. More particularly, the invention relates to an epoxy resin curing agent which has a low vapor pressure and has less odor and toxicity, an epoxy resin composition comprising an epoxy resin and the curing agent, and a cured product of the epoxy resin composition having high chemical resistance and improved mechanical characteristics.
2. Description of the Prior Art
Polyamines having an active hydrogen atom are utilized to a great extent in industry as a rapid curing agent for epoxy resins and providing a cured product with greatly improved physical properties as disclosed in, for example, U.S. Pat. Nos. 2,994,456 and 3,099,634. However, polyamines generally have a high vapor pressure and a strong irritating odor, and, in addition, there are various problems and health hazards such as a rash on human skin if the skin is irritated by the vapor polyamines give off. Attempts have been made to eliminate these disadvantages of polyamine curing agents by chemically modifying polyamines, for example, by reacting polyamines with epoxy group-containing compounds, acrylates, methacrylates, acrylonitrile, or aliphatic monocarboxylic acids, as disclosed in, for example, U.S. Pat. Nos. 2,890,204 and 3,205,054, but such a curing agent thus chemically modified had various defects such as an increase in the viscosity of a resin composition, which makes the curing agent difficult to handle, an impairment in the storage stability of the resin composition, or a considerable deterioration in the physical properties, such as mechanical strength and chemical resistance, of the cured product.
Another type of curing agent that has been proposed for epoxy resins to overcome the defects of polyamine curing agents is an acid anhydride curing agent as disclosed in, for example, U.S. Pat. No. 2,890,204, but as a matter of fact, an acid anhydride curing agent cannot be used as an alternative to a polyamine curing agent because a high temperature and a long time for curing are required.
U.S. Pat. No. 2,613,212 discloses 2-imidazolidones having on a ring nitrogen atom thereof an N,N'-alkylene substituent in which 2 acyclic carbon atoms separate two nitrogen atoms, with two types of such compounds being disclosed. However, there is no teaching or suggestion in U.S. Pat. No. 2,613,212 as to the ability of such compounds to cure epoxy resin compositions.